Method for the formation of semiconductor layer

Details Method for the formation of semiconductor layer Method for the formation of semiconductor layer

2000-12-13

2003-03-11

Kunemund, Robert (Department: 1765)

Single-crystal, oriented-crystal, and epitaxy growth processes;

Forming from vapor or gaseous state

With decomposition of a precursor

C117S090000, C117S094000, C117S095000, C117S096000, C117S103000, C117S106000, C117S951000

Reexamination Certificate

active

06530991

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for the formation of a semiconductor layer (or semiconductor layers), and more particularly to a method for the formation of a semiconductor layer (layers) suitable for applying in case of forming an epitaxial semiconductor layer (or layers) of, for example, a GaN (gallium nitride) or the like thin, thick or the like film(s) on a substrate or the like made of a variety of materials.
2. Description of the Related Art
In recent years, attention is being given to GaN being an nitride semiconductor of the groups III-V as a light-emitting device material in a short wavelength region such as blue wavelength region to ultraviolet wavelength region, and in this connection, blue light emitting diode (LED) prepared from a GaN system thin film material has been realized, besides developments for blue laser prepared from such GaN system thin film material are proceeding.
As such GaN system thin films, not only GaN, but also, for example, a light-emitting device material prepared from InGaN and the like are known.
In order to improve efficiency in light emission or to realize blue laser prepared from a GaN system thin film material, it has been considered to be important that structural defects, for example, mis fit dislocations, dislocations such as threading dislocations derived from misfit dislocations, grain boundaries and the like existing in a GaN system thin film are favorably controlled.
Meanwhile, a defect density (the number of structural defects per unit area) of a GaN thin film formed on sapphire (Al
2
O
3
)which has been widely used as a substrate indicates an extremely high value.
Such a high value of the defect density in GaN system thin film is principally due to lattice mismatch of a GaN system thin film with a substrate material (Al
2
O
3
) as well as a difference in thermal expansion coefficient between them. In this respect, a high value of defect density in a GaN system thin film has been considered to be an unavoidable problem in view of an actual status where no substrate which is appropriately used as a GaN substrate and which is in good lattice match with a GaN system thin film exists.
For the sake of improving a high defect density in a GaN thin film, as shown in
FIG. 1
illustrating schematically a thin film structure, such a manner that, for example, a 6H—SiC (0001) substrate being a type of SiC substrate is used, an AlN thin film is formed thereon (in a thickness of, for example, 10 nm or thicker), and a GaN system thin film is further formed thereon (in a thickness of, for example, 1.5 &mgr;m) has been applied heretofore.
Namely, since an AlN thin film has 1% of a rate of lattice mismatch with an SiC substrate, and on one hand, it exhibits a rate of lattice mismatch of 2.5% with a GaN thin film, such AlN thin film has been used as a buffer layer between the SiC substrate and the GaN system thin film.
In the thin film structure shown in
FIG. 1
wherein GaN having 1.5 &mgr;m thickness is formed on the AlN thin film having a thickness of 10 nm or thicker, although a dislocation density of 10
9
cm
−2
order was obtained as to threading dislocation in structural defects, it has been further desired to reduce remarkably dislocation density.
In view of such request, for instance, a manner of ELO (Epitaxial Lateral Overgrowth) process shown in FIGS.
2
(
a
) and
2
(
b
) has been lately proposed.
In the ELO process, first, crystal growth of GaN is made on a substrate
200
through a buffer layer
202
to form a first GaN layer
204
as a result of the crystal growth of GaN, and then, a mask
206
is formed on the first GaN layer
204
with the use of a predetermined mask pattern (see FIG.
2
(
a
)).
Thereafter, further crystal growth of GaN is made on the first GaN layer
204
on which has been formed the mask
206
to form a second GaN layer
208
, whereby it is intended to reduce a dislocation density of threading dislocations in the second GaN layer
208
(see FIG.
2
(
b
)).
According to the above described ELO process, threading dislocations appear in the first GaN layer
204
at a dislocation density of 10 to 10
10
cm
−2
order, while GaN crystal grown from the first GaN layer
204
which has not been covered by the mask
206
comes to grow laterally (directions indicated by the arrows in FIG.
2
(
b
)) on the mask
206
, so that a dislocation density of threading dislocations in the second GaN layer
208
was reduced to 10
7
cm
−2
order.
In the above described ELO process, however, it is required to form the mask
206
on the first GaN layer
204
with the use of a predetermined mask pattern (see FIG.
2
(
a
)). Accordingly, there have been such problems that a variety of processes of operation such as etching are required, whereby working hours extend over a long period of time as well as that its manufacturing cost and the like increase, so that the resulting products become expensive.
Moreover, there has been such a further problem that according to ELO process, threading dislocations appear in the second GaN layer
208
within boundary portions where GaN crystals each grown laterally by the use of the mask
206
fuse with each other (portions indicated by dotted lines in FIG.
2
(
b
)), so that when it is arranged in such that the second GaN layer
208
containing the boundary portions is not used for a device such as blue LED, a region of a GaN system thin film which can be used for a device and the like is restricted.
OBJECTS AND SUMMARY OF THE INVENTION
The present invention has been made in view of various problems involved in the prior art as described above, and an object of the invention is to provide a method for the formation of a semiconductor layer (layers) by which a defect density of structural defects, particularly a dislocation density of threading dislocations in the resulting semiconductor layer(s) can be remarkably reduced, so that hours of work can be shortened as well as a manufacturing cost can be reduced without requiring any complicated process in case of forming a semiconductor layer (layers) of, for example, a GaN (gallium nitride) or the like thin, thick or the like film(s) on a substrate or the like made of a variety of materials.
In order to achieve the above described objects, in the present invention, a method for the formation of a semiconductor layer for forming the semiconductor layer comprises supplying a structural defect suppressing material for suppressing structural defects in the semiconductor layer.
Therefore, according to the present invention, since a structural defect suppressing material for suppressing structural defects in a semiconductor is supplied, such structural defect suppressing material is adsorbed or applied at a position where a structural defect, and particularly threading dislocation appears on a surface of a material layer on which is to be formed the semiconductor layer, so that structural defects, particularly threading dislocations in the semiconductor layer are suppressed, whereby a dislocation density can be significantly reduced.
Furthermore, in the present invention, a method for the formation of a semiconductor layer for forming the semiconductor layer comprises supplying a structural defect suppressing material for suppressing structural defects in the semiconductor layer onto a surface of the layer of a material from which the semiconductor layer is to be formed.
Therefore, according to the invention, since a structural defect suppressing material for suppressing structural defects in a semiconductor is supplied onto a surface of the layer of a material from which the semiconductor layer is to be formed, the structural defect suppressing material is adsorbed or applied at a position where a structural defect, and particularly threading dislocation appears on a surface of the layer of a material on which is to be formed the semiconductor layer, so that structural defects, particularly threading dislocations in the semiconductor layer are suppressed, whereby a dislocation

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